A bomb ripped through a passenger train near New Delhi today, killing at least three people and injuring 19 others.

A bomb ripped through a passenger train near New Delhi today, killing at least three people and injuring 19 others, even as officials tightened security around the capital ahead of India's Independence Day celebrations.

The blast, caused by a crude bomb that officials believe may have been planted by separatist militants who have threatened to disrupt the national holiday, went off as the train was passing through Muradnagar station, 35 (20 miles north of New Delhi.

The condition of two of the injured passengers was described as ''serious'' by doctors.

The train, from the Hindu holy city of Hardwar, 125 miles away, was just an hour away from the capital when the bomb exploded .

Nobody has assumed responsibility for the blast. But authorities suspect separatist guerrillas in India's troubled northeast or Kashmir. The militants have called for strikes and threatened attacks during tomorrow's commemoration of India's independence from Britain in 1947.

Meanwhile, hundreds of thousandsoldiers were on high alert at major airports, railroad stations and other government buildings in response to the threats.

Authorities were taking no chances after the recent killings by suspected Islamic militants.

The 17th century Red Fort in New Delhi, where Prime Minister Atal Bihari Vajpayee is to speak, has been tightly guarded by security forces following intelligence reports of possible attacks by women suicide bombers.

Thousands of people were expected to attend the Red Fort ceremony.

Tourists have for five days been turned away from the Red Fort - home to the country's Mogul rulers for more than 200 years. Last December, two Kashmiri militants entered the fort and attacked an army supply depot there, killing two soldiers and one guard. The rebels escaped.

In the remote northeastern Indian state of Assam, some 20 guerrilla groups demanding independence or more autonomy have also threatened to disrupt Independence Day celebrations.

Pakistan celebrated its Independence Day on today. Giant banners in Islamabad, the Pakistani capital, described the disputed Kashmir territory as a humanitarian tragedy.

India and Pakistan have fought two of their three wars over Kashmir, which is divided between the two South Asian nuclear rivals. India accuses Pakistan of abetting terrorism by providing training and arms to the Islamic militants who have been fighting for an independent Kashmir or merger with Muslim Pakistan since 1989.

Pakistan denies the claim, saying it only offers moral and diplomatic support to the Islamic separatists.